1. Field of the Invention
The present invention relates to a four link suspension system for motor vehicles, and particularly to a structure for mounting upper control arms of the four link suspension system to a monocoque vehicle body having no frame.
2. Description of the Prior Art
In the four link suspension system, a rigid axle housing encasing an axle shaft for driving wheels, is connected to a vehicle body via a pair of upper control arms and a pair of lower control arms. Each control arm is pivoted at its forward end to the vehicle body and at its rearward end to the axle housing.
In the case of a monocoque body wherein brackets are provided on a floor panel of the body and the forward ends of the respective control arms are pivoted to the respective brackets, vibrations of the axle housing in a longitudinal direction of the body are directly transmitted via each control arm to the floor panel which is most susceptible to vibrations, thus leading to production of an undesirable inside noise of the vehicle.
There has been an attempt to prevent this inside noise by securing to both sides of the floor panel a pair of reinforcing outer side members to support the lower control arms and a pair of reinforcing inner side members to support the upper control arms, and pivotally connecting the forward ends of the respective control arms to the respective side members via brackets.
The lower control arms are disposed outside of the upper control arms, and the rearward ends of the lower control arms are pivoted to the rigid axle housing in the vicinity of the respective ends of the housing. In the vicinity of the ends of the rigid axle housing, no great deflecting vibration force will be exerted. Accordingly, the floor panel will not be vibrated so vigorously as to create an inside noise of the vehicle by the vibrations in a longitudinal direction transmitted from the lower control arms, via the outer side members, to the floor panel to which the outer side members are fixed.
On the other hand, the upper control arms are located inside of the lower control arms and the rearward ends of the upper control arms are pivoted to the axle housing inwards of the end portions to which the lower control arms are pivoted. The deflecting vibration force exerted to the axle housing exhibits a characteristic curve such that it is small at both ends of the axle housing and increases toward the inside. Accordingly, relatively strong vibrations will be transmitted to the foor panel from the rigid axle housing via the upper control arms and the inner side members, whereupon a great inside noise of the vehicle will be produced by the vibrations transmitted via the upper control arms.
It is conceivable to minimize the inside noise produced by the vibrations transmitted by the upper control arms in the above mentioned conventional mounting structure by pivotably connecting the rearward ends of the upper control arms to the axle housing at positions as close as possible to the outer ends thereof. In such a case, however, it is necessary to dispose the inner side members to which the forward ends of the upper control arms are pivoted, in the vicinity of the outer side members. This brings about various difficulties, for instance, such that the work for attaching the outer and inner side members becomes difficult. Thus, this system does not provide a satisfactory solution to the problem.